Photo-multiplier structure

ABSTRACT

Photo multiplier structure for a television camera-type storage vacuum tube, wherein a channel-type electron multiplier is employed which is sensitized principally only in a central area thereof which corresponds to the scanning area of the electron beam of an electron gun forming a part of the storage tube. This results in a substantial reduction of tube noise, eliminating overdriving of the preamplifier, and thereby providing increased sensitivity and resolution of the entire system.

[451. July 17, 1973 United States Patent [191 Beeli et al.

[ PHOTO-MULTIPLIER STRUCTURE [75] Inventors: Johann Battesta Beell,

Sylmar; Roger k; Philip GeorgeRelf, Chatsworth, all of Calif.

Henry Brown, Burban 10/1958 Great 313/65 A E U mm .O J. T wd n a W y r m u 8 flm SY flmc .mm a R0 P Hm w o.m mC m we m x e E r mmw .mmm Hm? m 0 v.. .GW mm 6 .7 mm mm kr a mC m. n m y mun w .m a A H H.

[22] Filed: Nov. 1, 1968 [211 App]. No.: 772,523

Kristofi'erson [57] ABSTRACT Photo multiplier structure for a television camera-type storage vacuum tube, wherein a channel type electron multiplier is employed which is sensitiz ed principally only in a central area thereof which corresponds to the 547 wa wa 1. m 3. 7 6 N6 1mm 1 W W m m L Mr. C10 M UhF 1]] 2 8 555 [[I oed mwmm w harm mnm m k m e w mrmm mm umw fk e h.m mu m m afi ye b i e mewh n .56 oeo mf Is 0 mm n e hm b esm e f n tm mm f wn o .m m anmmm eau M e 36.1w m m.m. m u mmm m f mfiaow mxxx ysss MMN 3333 M333 T m m m N m n m E m m T m m m m M M m u ML ll .1 a S mm m 2 m T. n e c e C n T a w S FBMH m E 5227 T 6666 II 9999 NHHHH U w HH 8726 01 1. m wwflfi 5 3 3333 3 Claims, 4 Drawing Figures Patented July 17, 1973 2 Sheets-Sheet 1 M w wwwww (LA/ANN B .BE'EL/ PHIL/P G. BE/F' Hesse H. Beow/v DR VE/V7025.

fiTroeA/EM Patented July 17, 1973 2 Sheets-Sheet 2 N 5.5 m T552 0 5 B w p Jean N Z y .wma @PB I PHOTO-MULTIPLIER STRUCTURE BACKGROUND OF THE INVENTION This invention relates to the storage tube art, and more particularly to storage tubes of the type wherein photo multiplication is accomplished by means of a channel-type electron multiplier interposed between the photo cathode and the storage target. Disclosures of channel-type electron multipliers of the general type to which the present invention is applied are found in US. Pat. No. 3,327,151, issued June 20, 1967, to .1. Adams and B.W. Manley for .Light Amplifier Employing an Electron Multiplying Electrode Which Supports a Photocathode; in an article by J. Adams and B. W. Manley in Electronic Engineering, March, 1965, page 108M181; and in an article by G.W. Goodrich and W. C. Wiley in Review of Scientific Instruments, 1962, Vol. 33, pages 761 and 762. It is to be understood, however, that the present invention is applicable to any channel-type electron multiplier employed in a storage tube.

The conventional channel-type electron multiplier is a glass disc which is perforated over the entire area thereof, the walls of the perforations being treated so that primary electrons from the photo cathode will produce a secondary electron emission ratio greater than unity as they pass through the perforations. The flat, parallel front and rear surfaces are conventionally coated over their entire areas with evaporated conductive layers to which an accelerating potential is applied.

Accordingly, the conventional channel-type electron multiplier disc is fully sensitized for electron multiplication over substantially its entire area.

Similarly, the storage target conventionally employed in a television camera-type vacuum tube is disc-shaped, having a functional area approximating that of the electron multiplier disc, the target being arranged closely adjacent and parallel to the electron multiplier, and coaxial therewith.

However, the scan pattern for the electron beam is rectangular in shape, covering only a central portion of the storage target, and accordingly only a similar central rectangular portion of the channel-type electron multiplier. The objective is to take an electrical output off of the target that is proportional to the stored potential on the target at the point of impact of the electron beam. However, with the conventional electron multiplier that is sensitized over the entire area of the disc, the grid will draw some current from peripheral portions of the multiplier outside of the scanned area, which produces an error voltage from the target and consequent tube noise. Additionally, this error voltage results in an undesirably high DC current from the target grid which tends to overdrive the preamplifier. The net result is that sensitivity and resolution of the system are reduced.

SU MMARY OF THE INVENTION According to the present invention the area of cooperation between the channel-type electron multiplier and the storage target is limited to an area corresponding substantially to the scan area of the electron beam, so as to substantially eliminate the production of error voltages in the peripheral region of the storage target outside of the scan area, and to reduce the DC current from the storage grid to substantially only that current resulting from the electron beam scan area so as to avoid overdriving of the preamplifier.

In one form of the invention, peripheral interaction between the electron multiplier and the storage target outside of the scan area is substantially completely eliminated by utilizing a channel-type electron multiplier having a cross-sectional area of channels which corresponds substantially only to the scanning area of the electron beam. In another form of the invention the peripheral interaction between the electron multiplier and the target is substantially completely eliminated by sensitizing only an area of the channel-type electron multiplier which substantially corresponds to the electron beam scan area.

The above-described and other advantages of the present invention will be better understood from the following description when considered in connection with the accompanying drawings.

BREIF DESCRIPTION OF THE DRAWINGS In the drawings, which are to be regarded as merely illustrative,

FIG. 1 is a side elevational view, partly in section, of a storage tube constructed in accordance with the present invention;

FIG. 2 is an enlarged sectional detail view of a portion of FIG. 1, illustrating one form of the invention wherein the channel-type electron multiplier employed therein has a cross-sectional area of channels only which corresponds substantially to the scanning area of the beam from the electron gun of the tube;

FIG. 3 is a plan view further illustrating the electron multiplier shown in FIG. 2; and

FIG. 4 is a plan view of a second form of electron multiplier according to the present invention, wherein the multiplier is sensitized only in an area corresponding substantially to the scanning area of the beam from the electron gun of the tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring at first to FIG. 1 of the drawings, a storage tube is indicated generally as 10, and includes an evacuated glass envelope 12. An electron gun is generally designated 14, and includes a tubular shell 16 having a suppressor grid 18 at its forward end as shown in FIG. 2. The electron gun 14 produces a scanning beam 20 of electrons.

A support ring 22 is connected to the forward end of the envelope l2, and includes a generally flat, circular portion 24 projecting radially outwardly as a flange from the forward end of envelope 12, and a tubular target support portion 26 upon which the storage target 28 is supported. Storage target 28 is a laminar structure composed of a fine metal screen 30 on the rearward side thereof which is scanned by the beam 20 of electrons, and a dielectric sheet 32 on the forward side thereof upon which an image is electrically stored.

The photo multiplier is generally designated'34, and is disposed forwardly of the storage target 28. Photo multiplier 34 includes a glass face plate 36 having an evaporated photo cathode 38 disposed on its rearward face, with a conductor ring 40 in electrical contact with the periphery of the photo cathode 38.

Disposed between the photo cathode 38 and the storage target 28 is a channel-type electron multiplier 42 having a perforate, disc'shaped glass body 44. The glass body 44 has evaporated electrodes 46 and 48 on its forward and rearward surfaces, respectively, through which the perforations extend. Conductor rings 50 and 52 are in contact with peripheral portions of the respective evaporated electrodes 46 and 48.

The face plate 36 and electron multiplier 42 are supported in properly spaced, parallel relationship with respect to the storage target 28 by a series of ceramic rings 54, 56 and 58.

The electron multiplier 42 illustrated in detail in FIGS. 2 and 3 is made according to a first form of the invention wherein the multiplier has a cross-sectional area of channels which corresponds in shape and size substantially to the scanning area of the electron beam 20. Thus, in this first form of the invention the perforations 60, which extend through the glass body 44 and evaporated electrodes 46 and 48 of the multiplier, are limited to a rectangular area 62 as shown in FIG. 3. Accordingly, the peripheral portion 64 of multiplier 42 that is located outside of the perforated rectangular area 62 is imperforate. By this means, the only part of the electron multiplier 42 which is capable of functioning as a mutliplier, or in other words is sensitized, is the rectangular, perforate area 62 which corresponds substantially to the scan area of the electron beam 20. Consequently, there is no material interaction between the peripheral portion 64 of the electron multiplier disc and the storage target 28, whereby undersired error voltages are substantially completely eliminated from the peripheral portion of the storage target 28 outside of the scanned area.

In the first form of the invention shown in FIGS. 2 and 3, the evaporated electrodes 46 and 48 of the multiplier may fully cover both of the flat surfaces of the disc-shaped glass body 44, except for the perforations in the rectangular area 62, although all that is required for operation of this form of the invention is that the evaporated electrodes 46 and 48 be disposed in the rectangular area 62, and that conductive paths extend outwardly therefrom to the respective conductor rings 50 and 52.

According to the second form of the invention that is illustrated in FIG. 4, the electron multiplier 42a has a disc-shaped glass body 44a which is perforated over its entire area, but is provided with front and rear evaporated electrodes which are substantially coextensive with the area that is scanned by the electron beam 20. Thus, with the conventional rectangular scanned area, the front electrode 46a, which is seen in the plan view of FIG. 4, will be rectangular, and have an area which corresponds substantially only to the scanning area of the electron beam. Similarly, the rear electrode will be rectangular and coextensive with the front electrode 460; accordingly, the rear electrode is not seen in the plan view of FIG. 4, as it is directly underneath the front electrode 460. Thus, even though the glass body portion 44a of the electron multiplier 42a is perforate over substantially its entire area, nevertheless, the mutliplier 42a is only sensitized in an area substantially corresponding to the scanning area of the electron beam, whereby peripheral error voltages are greatly minimized, or substantially completely eliminated.

In the second form of the invention that is illustrated in FIG. 4, conductive paths 66 may extend radially outwardly from opposite sides of the rectangle 46a, terminating in peripheral contact strips 68 which engage the conductor ring 50. The conductors 66 and contact strips 68 may consist of evaporated coatings on the front surface of the glass body 440. Similarly, conductor strips 70 may extend radially outwardly from opposite sides of the rectangular electrode on the rear surface of the glass body 44a, ending in peripheral contact strips 72, the conductors 70 and contact strips 72 preferably being offset from the respective conductors 66 and contact strips 68, whereby the only area of the multiplier 42a which has full, opposed electrode surfaces is the rectangular area 46a. Accordingly, the electron multiplier 42a is only effectively sensitized in the rectangular area corresponding to the scanning area of the electron beam.

While the instant invention has been shown and described herein in what are conceived to be the most practical and preferred embodiments, the invention is of course not limited to those specifically described. Many changes and modifications of the invention will suggest themselves to those skilled in the art. The true scope of the invention is therefore defined only in the appended claims.

What is claimed is:

1. In an electron discharge device, the combination comprising: an evacuated substantially cylindrical envelope having a circular end face; a photocathode bonded to the interior surface of said end face; an electron multiplier positioned inside said envelope and fixed relative thereto, said multiplier having a circular disc shape with one flat surface parallel and adjacent to said photocathode, and another flat surface parallel to said one surface; an electron gun positioned inside said envelope and fixed relative thereto; first means for transmitting signals to said gun to cause said gun to produce a flow of electrons only inside of a closed curve at a predetermined distance from said gun, said multiplier including a dielectric body having holes extending completely through said body and interrupting both of said flat surfaces, said holes having surfaces which will support secondary emission at a ratio greater than unity; a planar target parallel to and adjacent to said other flat surface, said target having a first surface intercepting the electrons emanating from said gun, said first surface having a rectangular area thereon bounded by said curve, said curve projection being normal to said target, said first means being adapted to cause said gun to make a raster-type scan wholly within said curve with a pencil beam; and second means to prevent electron flow out of said multiplier outside a projection of said curve thereon.

2. The invention as defined in claim 1, wherein said body has an evaporated electrode bonded to each side thereof, said electrodes having holes therethrough in registration with said body holes, each of said electrodes being bounded by a curve identical to said closed curve, said closed curve on said target having an axis of symmetry normal to said first surface through the center of said closed curve, both of said electrode boundaries having the same said axis of symmetry as that of said closed curve, each of said electrodes having connecting portions electrically connected thereto and extending outside of the respective curves, said connecting portions be spaced sufficiently that no line normal to said body surfaces intersects both of said portions, said portions being T-shaped, the cross of each T being arcuate and contiguous to the circular edge of said body, the vertical of the Ts being symmetrical with one corresponding side and end of the rectangle.

6 ular to said one and other flat surfaces, said body thereby having a border around said rectangular areas which is made of a solid dielectric, said border having I a minimum width which is substantially larger than the space between said holes. 

1. In an electron discharge device, the combination comprising: an evacuated substantially cylindrical envelope having a circular end face; a photocathode bonded to the interior surface of said end face; an electron multiplier positioned inside said envelope and fixed relative thereto, said multiplier having a circular disc shape with one flat surface parallel and adjacent to said photocathode, and another flat surface parallel to said one surface; an electron gun positioned inside said envelope and fixed relative thereto; first means for transmitting signals to said gun to cause said gun to produce a flow of electrons only inside of a closed curve at a predetermined distance from said gun, said multiplier including a dielectric body having holes extending completely through said body and interrupting both of said flat surfaces, said holes having surfaces which will support secondary emission at a ratio greater than unity; a planar target parallel to and adjacent to said other flat surface, said target having a first surface intercepting the electrons emanating from said gun, said first surface having a rectangular area thereon bounded by said curve, said curve projection being normal to said target, said first means being adapted to cause said gun to make a raster-type scan wholly within said curve with a pencil beam; and second means to prevent electron flow out of said multiplier outside a projection of said curve thereon.
 2. The invention as defined in claim 1, wherein said body has an evaporated electrode bonded to each side thereof, said electrodes having holes therethrough in registration with said body holes, each of said electrodes being bounded by a curve identical to said closed curve, said closed curve on said target having an axis of symmetry normal to said first surface through the center of said closed curve, both of said electrode boundaries having the same said axis of symmetry as that of said closed curve, each of said electrodes having connecting portions electrically connected thereto and extending outside of the respective curves, said connecting portions be spaced sufficiently that no line normal to said body surfaces intersects both of said portions, said portions being T-shaped, the cross of each T being arcuate and contiguous to the circular edge of said body, the vertical of the T''s being symmetrical with one corresponding side and end of the rectangle.
 3. The invention as defined in claim 1, wherein said body is perforated only through rectangular areas through said one and other flat surfaces, said rectangular areas being identical to that bounded by said closed curve, a line passing through the center of said closed curve perpendicular to said first surface also passing through the center of said rectangular areas perpendicular to said one and other flat surfaces, said body thereby having a border around said rectangular areas which is made of a solid dielectric, said border having a minimum width which is substantially larger than the space between said holes. 